Laser calibration and stabilization algorithm for microscopy device

Abstract

A method, system, and computer program product for determining calibration parameters for controlling the intensity of a laser diode are provided. An example method may include determining a slope representing a relation of a change in a photodiode output value to an input current transmitted to the laser diode. In the example method, the photodiode output value is received from a monitoring photodiode positioned to receive light from the laser diode, wherein the photodiode output value corresponds to the intensity of light generated by the laser diode and received at the monitoring photodiode. The example method further includes selecting an operating photodiode output value based at least in part on the slope, wherein the operating photodiode output value corresponds to a target photodiode current at the monitoring photodiode during operation.

1 . A method for controlling an intensity of light from an illumination source, the method comprising:
 determining a slope representing a relation of a change in a photodiode output value received from a monitoring photodiode to a change in an input current transmitted to the illumination source,
 wherein the photodiode output value corresponds to the intensity of the light received at the monitoring photodiode; and 
   selecting an operating photodiode output value based at least in part on the slope.   
     
     
         2 . The method of  claim 1 , further comprising adjusting the input current transmitted to the illumination source to maintain a real-time photodiode output value at or near the operating photodiode output value. 
     
     
         3 . The method of  claim 2 , wherein adjusting the input current provided to the illumination source further comprises:
 receiving a measured photodiode output value;   comparing the measured photodiode output value to the operating photodiode output value;   determining a difference between the measured photodiode output value and the operating point photodiode output value; and   in an instance in which the difference is greater than a unit step size, adjusting the input current.   
     
     
         4 . The method of  claim 1 , where determining the slope comprises:
 determining an input current difference representing a difference between a first input current and a second input current;   determining a photodiode output difference representing a difference between a first photodiode output value and a second photodiode output value,
 wherein the first photodiode output value corresponds to the first input current and the second photodiode output value corresponds to the second input current; and 
   determining a ratio between the input current difference and the photodiode output difference.   
     
     
         5 . The method of  claim 4 , wherein selecting the operating photodiode output value further comprises:
 determining a plurality of slopes, each slope corresponding to a different range of input currents and corresponding range of photodiode output values; and   selecting the operating photodiode output value within the range of photodiode output values corresponding to the range of input currents and corresponding range of photodiode output values having a steepest slope.   
     
     
         6 . The method of  claim 1 , wherein the illumination source is a laser diode having an input current threshold corresponding to a minimum input current at which the laser diode will produce coherent light. 
     
     
         7 . The method of  claim 6 , further comprising:
 determining a linear approximation of a portion of a photodiode output current curve based at least in part on the slope and the operating photodiode output value,
 wherein the photodiode output current curve represents the relation of the input current to the photodiode output value; and 
   determining the input current threshold based on an intersection point at which the photodiode output value of the linear approximation is zero.   
     
     
         8 . The method of  claim 7 , wherein the operating photodiode output value is selected by scaling the input current threshold by a pre-determined operating point scale factor. 
     
     
         9 . The method of  claim 8 , wherein the operating point scale factor is between 1.4 and 1.6. 
     
     
         10 . The method of  claim 6 , wherein the input current threshold and the operating photodiode output value are stored in a memory storage device. 
     
     
         11 . The method of  claim 1 , wherein the input current is controlled by a potentiometer. 
     
     
         12 . A system comprising:
 an illumination source;   a monitoring photodiode positioned to receive light from the illumination source; and   a controller comprising a processor and an instruction memory including program code, the instruction memory and program code configured to, with the processor, cause the message handler processor to:
 determine a slope representing a relation of a change in a photodiode output value received from the monitoring photodiode to a change in an input current transmitted to the illumination source;
 wherein the photodiode output value corresponds to the intensity of light received at the monitoring photodiode; and 
 
 select an operating photodiode output value based at least in part on the slope. 
   
     
     
         13 . The system of  claim 12 , wherein the controller is further configured to adjust the input current transmitted to the illumination source to maintain a real-time photodiode output value at or near the operating photodiode output value. 
     
     
         14 . The system of  claim 12 , wherein determining the slope comprises:
 determining an input current difference representing the difference between a first input current and a second input current;   determining a photodiode output difference representing the difference between a first photodiode output value and a second photodiode output value,
 wherein the first photodiode output value corresponds to the first input current and the second photodiode output value corresponds to the second input current; and 
   determining a ratio between the input current difference and the photodiode output difference.   
     
     
         15 . The system of  claim 14 , wherein determining the operating photodiode output value further comprises:
 determining a plurality of slopes, each slope corresponding to a different range of input currents and corresponding range of photodiode output values; and   selecting the operating photodiode output value within the range of photodiode output values corresponding to the range of input currents and corresponding range of photodiode output values having a steepest slope.   
     
     
         16 . The system of  claim 12 , wherein the illumination source is a laser diode having an input current threshold corresponding to a minimum input current at which the laser diode will produce coherent light. 
     
     
         17 . The system of  claim 16 , wherein the controller is further configured to:
 determine a linear approximation of a portion of a photodiode output current curve based at least in part on the slope and the operating photodiode output value,
 wherein the photodiode output current curve represents the relation of the input current to the photodiode output value; and 
   determine the input current threshold based on an intersection point at which the photodiode output value of the linear approximation is zero.   
     
     
         18 . The system of  claim 17 , wherein the operating photodiode output value is selected by scaling the input current threshold by a pre-determined operating point scale factor. 
     
     
         19 . The system of  claim 12 , further comprising a potentiometer communicatively connected to the controller and electrically connected to the illumination source, wherein the controller controls the input current to the illumination source by transmitting an electrical signal to the potentiometer. 
     
     
         20 . A computer program product for controlling an intensity of an illumination source, the computer program product comprising at least one non-transitory computer-readable storage medium having computer-readable program code portions stored therein, the computer-readable program code portions comprising an executable portion configured to:
 determine a slope representing a relation of a change in a photodiode output value received from a monitoring photodiode to a change in an input current transmitted to the illumination source,
 wherein the photodiode output value corresponds to the intensity of a light received at the monitoring photodiode; and 
   select an operating photodiode output value based at least in part on the slope.